Inhibiting biological growths in acidic photographic processing solutions with nitro alcohols



United States Patent US. Cl. 96--60 5 Claims ABSTRACT OF THE DISCLOSURE Biological growth in photographic processing solutions such as ferricyanide bleach solutions is inhibited by the use of nitro alcohols.

This invention relates to the prevention of biological growths in photographic processing solutions.

Biological growths have created a problem for many years in the household, agriculture and industry. Means for combating the biological growths have varied widely since a biocide must be selected which is innocuous to the product under consideration. Thus, a biocide useful in the treatment of agricultural products may be totally unsuitable for industrial use. In the photographic industry, biological growths take place in the various processing solutions with the result that the chemistry of the process may be adversely affected and a dirt problem may arise. While bacteria and fungi frequently grow best in neutral solutions, they grow well in acid solutions such as the well-known acid ferricyanide bleach solutions, acid hardener and washing solutions containing acid used in photography.

Many biocides known to be useful for controlling the growth of fungi or bacteria were examined and were not found to generally inhibit the growth of bacteria and fungi or the growth of specific strains such as Arthrobotrys fungus which appeared in certain motion-picture laboratories. On the other hand, certain biocides found to be effective against such strains of fungi were incompatible with the acid processing solutions, i.e., they adversely affected the sensitometric properties of the photographic images, or they caused dye images to be unstable or the biocides were unstable in processing solutions.

We have discovered that the growth of both fungi and bacteria in acid photographic processing solutions is strongly inhibited by the use of aliphatic nitro alcohols in the solutions. Moreover, these compounds are compatible with the photographic processes and particularly processes involving color development. It appears that the nitro alcohols attack the cellular protein of the bacteria and fungi and release a substance which inhibits the activity of cellular enzymes controlling growth. Accordingly, it is believed that species resistance should not develop with continued use of the nitro alcohols. This is contrary to the activity of a bactericide such as boric acid which had been found to be satisfactory for use in ferricyanide bleach solutions until the mentioned strain of fungus appeared, the growth of which was not controlled by boric acid. The nitro alcohols such as the nitropropanediols can be used in alkaline photographic developers and wash waters to inhibit biological growth. However, the problem is usually not as serious.

The nitro alcohols most useful for inhibiting biological growth in the acid processing solutions are the nitroethanols and nitropropanol such as l-nitroethanol, 2-nitroethanol, 2-methyl-2-nitro-l-propanol and particularly the 2 nitro 1,3 propanediols including 2-hydroxymethyl-2- nitro 1,3 propanediol, 2-methyl-2-nitro-1,3-propanediol Patented Nov. 24, 1970 and 2-ethyl-2-nitro-1,3-propanediol. Very useful 2-nitro- 1,3-propanediol compounds are characterized by substitution of the carbon atom in the 2-position by both the nitro group and for example, by lower hydroxyalkyl, lower alkyl, phenyl, substituted phenyl and the like. Accordingly, representative nitro alcohols useful in the invention have the general formula R and R each represent hydrogen or a substituent such as lower alkyl and substituted lower alkyl such as hydroxyethyl, phenyl and substituted phenyl such as chlorophenyl, etc.

The nitro alcohols are especially useful as biocides in the acid ferricyanide bleach solutions. These solutions are well known in the art and are employed to rehalogenize silver in photographic emulsion layers or other layers so that the resulting silver salt can be removed from the layers by treatment with conventional acid fixing solutions. Thus, in a well-known process of color development a multilayer color film containing color forming coupler compounds in the layers is developed with a color developing solution to produce silver and dye images in the layers. An acid ferricyanide bleach solution containing the nitro alcohol is then employed to convert the silver in the layers to silver halide for subsequent removal with acid fixing solution.

The following acid ferricyanide bleach solution is representative of the acid processing solutions in which the nitro alcohols are effective for inhibiting biological growth:

Gms. Potassium ferricyanide 50 Potassium bromide 40 2-hydroxymethyl-2-nitro-1,3-propanediol 0.1

Water to 1 liter. pH adjusted to 6.5 with sodium hydroxide or sulfuric acid.

This solution is used in a conventional tank color development process for motion picture film at a temperature of about F. to bleach the silver images until the solution is exhausted. Fresh bleach solution is then placed in the tank. Over a period of several months no appreciable biological growth is found on the walls of the tank or processing equipment in the tank, whereas previously in a particular processing area, in absence of the propanediol compound significant amounts of Myxobacteriales or Enterobacterioceae bacteria and Fusarium or Arthrobotrys fungi appeared.

Other ferricyanide bleach solutions in which the nitro alcohols can be used to inhibit biological growths are disclosed in US. Pats. 2,640,775, 2,662,014, 2,611,699, 2,763,550, 2,611,700, 3,189,452 and 2,943,935.

The nitro alcohols, especially the 2-nitro-1,3-propanediols, are also useful for inhibiting biological growth in other acid photographic processing solutions such as an aldehyde bisulfite hardening bath pH 6.0, a neutralizer solution pH 6.0 containing an amine such as disclosed in Blackmer et al., US. Pat. 3,168,400, an ammonium thiosulfate stop and fixing solution pH 4.0 and in an ammonium thiosulfate fixing solution pH 6.8. 2-hydroxymethyl-Z-nitro-1,3-propanediol is effective in these solutions at a concentration of 2.5 g./l. without adverse effect on the chemistry of the process.

In the above ferricyanide bleach solution from about 0.01 to 6.0 or more grams per liter of the compound 2- hydroxymethyl-Z-nitro-1,3-propanediol are useful for inhibiting biological growths. Similar amounts of one or more of the other nitro alcohols can be used in the bleach solution and in the above acid processing solution, depending in part upon the susceptibility of the organisms involved, the acid solution involved and the activity of the paritcular nitro alcohol under consideration. The optimum amount to use in the selected solution with the organisms present is readily determined by comparing the growth in the solution containing the nitro alcohol with growth in a control solution, at the end of about one month to observe the growth of fungus, and every other day or so for bacterial growth.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected Within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. In a photographic process comprising the steps of developing an exposed photographic element and bleaching the exposed and developed element with an acidic ferricyanide bleach solution, the improvement which comprises employing in said bleaching step an aqueous acidic ferricyanide bleach solution containing a nitro alcohol selected from the group consisting of the nitroethanols and the nitropropanols in an amount suflicient to inhibit biological growths in said solution.

2. A process as described in claim 1 wherein said nitro alcohol is a 2-nitro-1,3-propanediol.

3. A process as described in claim 1 wherein said nitro alcohol is selected from the group consisting of 2-hydroxymethyl-Z-nitro-1,3-propanediol, 2-methy12-nitro-1,3-propanediol, 2-ethyl-2-m'tro-1,3-propanediol and 2-methyl-2- nitro-l-propanol.

4. A process as described in claim 1 wherein said nitro alcohol is 2-hydroxymethyl-2-nitro-1,3-propanediol.

5. A process as described in claim 1 wherein said nitro alcohol is present in said solution in an amount of from about 0.01 to about 6 grams per liter of solution.

References Cited UNITED STATES PATENTS 2,364,017 11/1944 Baldsiefen 9667 OTHER REFERENCES Ilford: Manual of Photography, 1958 pp. 532-538.

NORMAN G. TORCHIN, Primary Examiner M. KELLEY, Assistant Examiner US. Cl. X.R. 9650, 61, 62 

